Manitoba Agriculture, Food and Rural Initiatives

Unworked Corn Fields Going into 2009 - Friend or Foe?

The 2008 corn harvest is for the most part complete. Taking into consideration the lack of field work accomplished on harvested corn fields and high levels of corn stover/residue remaining, we may see a large number of producers deciding to burn the stover. However, will producers wonder how much money in nutrient loss will go up in smoke? With the increasing costs of fertilizer, that is a question producers should give some serious consideration to before striking that match.

There is no Manitoba-based data that I’m aware of that quantify nutrient loss caused by burning corn stover. However, a study by John Heard and Curtis Cavers from Manitoba Agriculture, Food and Rural Initiatives looked at nutrient loss from cereal stubble when burned. For comparison sake, we will assume the nutrient loss will be similar between cereal stubble and corn stover.

Heard and Cavers found producers lost 95% of the nitrogen, 25% of the phosphorous, 35% of the potassium, and 75% of the sulphur in the cereal stubble when it was burned. Now, if we look at what nutrients are available in stover from a 159 bushel per acre corn crop, there are 33 lbs of N/acre, 11 lbs of P/acre, 97 lbs of K/acre, and 4 of lbs S/acre available. So, what this translates into is producers are losing 31 lbs N, 3 lbs P, 34 lbs K, and 3 lbs S per acre when they burn their corn stover!

If we go one step further and figure out the value of that nutrient loss, if we assume that N is $0.65 per lb, P is $0.90 per lb, K is $0.65 per lb, and S is $0.75 per lb (based on a price survey in November 2008 and an average of anhydrous, liquid and granular fertilizers), producers are losing $20.15 per acre of N, $2.70 per acre of P, $22.10 per acre of K, and $2.25 per acre of S. That’s a total of $47.20 per acre worth of nutrients going up in a thick, black smoke.

If the value of nutrient loss isn’t enough to convince producers not to burn their stover, there are also other reasons to consider when deciding to burn or not to burn.

• Any cover producers can leave will help prevent valuable topsoil from blowing away. Having productive soil in the ditch won’t help early emergence due to supposed increased soil warming from a dark soil surface in the spring.
• The stubble can help improve organic matter content in the soil, which improves physical properties, including increased water-holding capacity, as well as the supply and availability of nutrients (N, P, S, and micronutrients held in organic forms).
• Burning corn stover will not help to decrease future corn borer infestations.
• Corn borer larvae can survive and overwinter in unburned stalks and those larvae can cause a severe infestation under suitable conditions.
• Burning of corn stover will also not decrease disease pressure, such as stalk rots or leaf diseases.

Burning stover might be a quick and easy way to prepare fields for the 2009 season. However, producers should look at the stover as a potential investment of $47.20 per acre worth of nutrients.